This invention relates to a method for the dry-forming of paper, of the kind in which cellulose fibers suspended in a stream of air are deposited onto an air-pervious web under the action of vacuum, thus forming a layer of fibers; the thus formed layer of fibers being then suitably pressed and compacted by means also of a suitable adhesive binder.
More particularly, this invention relates to an apparatus or head for depositing the fibers onto said web for the formation of the layer of fibers.
Some types of heads for depositing the fibers onto a formation web are known. Thus, for example, in the U.S. Pat. No. 3,581,706 filed on Nov. 13, 1969 and granted on June 1, 1971 to Mr. Karl Kristian Kobs Kroyer there is shown and described a formation head of the type disclosed above, comprising a cylindrical housing provided with a bottom flat perforated wall, with an inlet opening for a stream of air having fibers suspended therein, and provided in the interior thereof with a stirrer comprising one or more rotating stirring blades suspended at a short distance from said bottom wall, so mounted as to perform--together with the rotary motion about their axis--a circular translatory movement around the axis of the formation head.
One of the disadvantages of this formation head resides in the fact that due to the movement of the stirrers parallelly to the bottom wall, said bottom wall is liable to become clogged. Moreover, the planetary movement of the stirrers implies the arrangement, in the interior of the head, of very delicate drive members liable to be damaged or broken.
The European Patent Application No. 812000586 filed on Jan. 16, 1981 in the name of Scanweb I/S discloses a formation head comprising two cylindrical parallel perforated chambers, each provided in the interior thereof with a cylinder having radial needles thereon and tangent to one of the directrices of said chambers. Each chamber rotates around its axis, and the cylinder associated therewith rotates in the opposite direction around its axis. The fiber-entraining stream of air is fed into the interior of said cylindrical chambers, and the fibers outflowing from said cylindrical chambers are deposited onto the underlying formation web.
This formation head is relatively complicated and each head requires at least two distributing chambers and, nevertheless, the distribution onto the underlying cloth is scarcely uniform.
The U.S. Pat. No. 4,157,724 filed on Dec. 19, 1977 and granted on June 12, 1979 to Torsten B. Persson discloses a formation head substantially comprising a V-shaped reticulated bottom extending transversely to the formation web. Mounted within said container are stirrers for stirring the fibers being fed into said container so as to hurl them against said reticulated bottom and move them therealong to pass through the network thereof and deposit them onto the formation cloth. According to this formation head, said reticulated bottom extends laterally upwards to permit said stirrers to operate as well at the periphery of the network. However, this creates problems of uniform distribution. Moreover, due to the inherent mode of the operation of this head, the fibers are separated from the fiber-entraining stream of air before being fed into the head.